I don't know what kind of base is on mine. It too was with the gun when I bought it. The only marking I can find without taking it of is a circle with an R in it. It does stick over the chamber port on both ends about 1/4" but nothing too get too worked up about. I guess it's got a rear windage adjustment in that there is a screw on each side of the base. And if you want to slide the base over one way or the other you loosen one screw and tighten the other. (Leupold STD Mount?) The rings that are on it are Burris signature series rings with the inserts. I figured if I needed more elevation out of the rings/base setup I could put in offset inserts.